It’s common to see this written as three steps: SELECT balance FROM accounts WHERE user_id = 1; -- in the application, subtract 100 from balance if it's above -- 100; and, where ?is the new balance: UPDATE accounts SET balance = ?Object/relational mappings are usually defined in an XML document.The mapping document is designed to be readable and hand-editable.
I often have people on Stack Overflow ask things to the tune of “Don’t transactions prevent this? Unfortunately, while great, transactions aren’t magic secret sauce you can add for easy concurrency.
If they are specified, tablenames will be qualified by the given schema and catalog names.
If they are missing, tablenames will be unqualified. It is, however, good practice (and expected by some tools) to map only a single persistent class, or a single class hierarchy, in one mapping file and name it after the persistent superclass.
To support optimistic locking, the AWS SDK for Java provides the annotation.
In the mapping class for your table, you designate one property to store the version number, and mark it using this annotation.